Motor operated tap changer



Aug. 1943- H. J. CARLIN ETAL 2,447,634

MOTOR OPERATED TAP CHANGER Filed April 14, 1944 2 Sheets-Sheet 1WITNESSES: lNVENTOR' ATTORNEY 1948- H. J. CARLIN ETAL moron OPERATED TAPCHANGER 2 Sheets-Sheet 2 Filed April 14, 1944 a 3 wk 3 Q M,

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A Chapman.

Z. W ATTORNEY Patentel Aug. 24, 19485 so srATss ss'rsur oss cs MQTOEOPERATED TAP CHANGER Herbert Carlin, East 0551238: and James Chapman,Madison, be, m, assagnors to Woo haghouse Electric fin'pol'ation EastPittsburgh. 39s., a corporation oi Pennsylvania Application April M, @42, Non 53%9925 9? Claims i, The invention relates to regulator systems,is illustrated as applied. to electrical apparatus for regulating thevoltage e distribution cit outiozi systems for suopiying 'ous loaddevices, autometi such as ta o employee.

age which is effective to .& ti te the tion i so nism 1oz raising andlower? one voltage of he supply circuit as this voltage drops below orrises above a desires value,

When a tap-changing operation has been initiated. by operation of theprimers relay, the tap-changing mechanism is operated through c step inthe operation of the mechanism chenglog the output voltage apredetermined. ci'count corresponding to that efiecteci by changing thepoint oi connection from one ton connection to the next in a series oftoo connections. The voltage change on the regulated circuit may not beeffected rapidly enough to cause the primers relay contacts to interruptthe opereti tsp-changing mechanism u ichanging step, but may coiltinthrough a second step before previously completed step of operctioemechanism has been felt on relezv operating winding, Thus a false stepo2 tion is initiated. This over=resuietion circuit results in anotl roperation of the regulater in the opposite direction to correct circuitcondition and, ii the regulator continues to over-regulate in bothdirections, will cause the regulator to operate back anal forth betweenadjacent tap positions of the regulator causing unnecessary wear andtear on the sresulzsiting apparatus.

One way of preventing this I hunting operation of the regulator is v,the tapchanging mechanism for an appreciable time at the end of eachtap-changing operation, so that sufficient time will elapse for theWinding oi the pric relay to respond to the voltage change on the systemresulting from the tap-changing operation before a further tap-changingoperatlon occurs. It is, however, undesirable to do coerc this thecondition oi the regulated circuit requires operation of the regulatorthrough several. tap-changing steps in order to effect a correclci,

tics inthe regulates. (quantity the circuit its desired value.

In accor' provisos. mery relay control c voltage of the ciicu Leliaintroducing en otlclit'ionsf. volts,

the primary relay conceal e invention, means direction to tep eioengineor? the opere coa ition -i compo e c 'c t, cousins; the primers to imecllotely; become egein responsive to the regulov age. It the comclitionto be regulated requires other operation of the regulator in the on-cticn, the pri mery relay will again close its contacts and efiect suchoperation. It? the voltage change required is large, requiring severaltop-changing steps in the operation of the reg sister; bias may not besufiicient to separate the relay contacts duo mg every step oiopei'etioo oi regulator, he cause the force tending to keep the contactsclosed will also be large, but the contacts will he seperetecl soonenough to prevent overtrsvei in the operation of the res later.

It is an object of the invention to provide a regulator system of theshove-indicated chemo-=- ter that is provided with means for preventingovestravel oil the regulatin apparatus.

More specificalkv stated it is an object oi; the invention to introduceso anti-hunting ZlEtlQIl into the operation of the primary relsinitiating the operation or the regulating apparatus during theoperation of the regulating mechanism, and to remove the anti-detectingaction immediately upon completion of 2, step of operation of theregulator to again permit immediate control of the regulator by theprimary relay, in accordance with the conditions all the circuit lacingregulated.

@ther objects and advantages or the inventlon will become apparent fromthe following description of a preferred embodiment thereof, referencebeing lied to the accompanying; ores-v ings, in which:

Figure l is a. diagrammatic view oi apparatus and circuits illustratingone preferred embodiment of the invention;

Fig. 2 is a simplified diagram oi" the control circuits shown in Fig. 1;

Fig, 3 shows curves illustrating cclcsistes variations in primary relaycurrent under certain conditions of the circuit; and

Figs. 3A and 3B are diagrammatic simplifications of the. anti-huntingcircuit.

Referring to the drawings, conductors i, 2 and 3 represent a three-phasealternating-current power circuit connected to primary transformerwindings 4, 5 and 6 that are inductively related, respectively, towindings i, t and 9, through which energy is supplied to the three-phasecir cuit represented by conductors ii, i2 and 53. A tap-changingmechanism is provided for varying the voltage ratio between the primarycircuit conductors i, 2 and 3 and the secondary circuit conductors H, i2and it which is diagrammatically illustrated as comprising a pluralityof tap-changing switch contact members l4 connected to the tap points inthe secondary windings I, 8 and 9, and cooperating -with movable switchcontact members in in each of the three phases that are similarlyoperated by a mechanism diagrammatically illustrated as an arm I 6controlled by a screw-threaded shaft i! that is operated throughsuitable gearing mechanism l8 by motor l9.

Control means for the tap-changing mechanism is provided comprising acircuit controller or primary relay which is effective to control theoperation of the secondaryrelays 22 and it to cause operation of themotor it in the one or in the other direction. The auxiliary relays 2tand 25 are controlled upon the operation of the motor l9 to introduce ananti-hunting action into the operation of the primary relay 2%.

The relay 20 is provided with an operating winding 26 that is connectedin series with the winding 21 of a reactance device 228 that isconnected by conductors 3! and 32 to be energized in accordance with thevoltage across the-conductors l2 and 63. A potential transformer may beprovided for energizing this circuit from the circuit conductors l2 andit if desired.

The relay 20 is shown as of the induction type, and comprises amagnetizable core structure having an outer ring 33, an upwardlyprojecting center leg 34 and two downwardly extending spaced legs 35 and36. The main operating winding 28 and also the winding 38 is provided onthe leg 34, the winding 38 being connected in series circuit relationwith windings 39 and at carried on the legs 35 and 36, respectively.Auxiliary compen sating windings 4| and #32 are also carried on the legs35 and 36, respectively, and are connected in series circuit relationwith each other and energized in accordance with the load on the circuitas determined by the current transformer 48 connected to the windings Mand 432 by circuit conductors 49. An adjustable resistor 56 is includedin this circuit for adjusting the degree of line drop compensationdesired.

As illustrated, a movable disc 43 of copper or other suitable conductingmaterial is rotatably mounted between the ends of the pole pieces orprojecting legs of the magnetic circuit, the disc being disposed to bemoved in the one or the other direction depending upon the energizationof the windings of the relay. When the disc 43 is moved, a contactmember 44 carried at the upper end of the shaft 45 is actuated to engagethe one or the other of the stationary contact mem- 'bers 46 or 41, tocontrol the operation of the secondary relays 22 or 23, depending uponthe direction of movement of the contact member ti As is usual practice,a spring (not shown) is provided for biasing the'shaft at a direction tobias the contact member 44 toward or into engagement with the-contactmember 48. The

, spring is so adjusted that it will establish the value of theregulated quantity to which the relay-20 is responsive. Permanentmagnets 53 and 54 are shown positioned to retard the movement of thecopper disc d3, so as to provide a time-delay operation of the relay 2!]that varies inversely as the change in the voltage applied to'the relayenergizing circuit comprising conductors 3| and 32,

. as the disc 43 is moved in response to the (litterence between theforce of the spring and that induced by the relay windings.

The" primary relay 20 may correspond to that disclosed in Patent No.2,313,921, issued March 16, 1943, to H. J. Carlin and L. N. Crichton forRegulator control equipment, assigned to the same assignee as thisinvention.

The supply conductors i2 and I3 are connected to be energized fromconductors i2 and It, to provide a supply of energy for operating themotor is and the relays 22, 23, 24, and 25. If the regulated voltagedrops below its desired value, the relay 2!! will operate to bring thecontact member 44 into engagement with the contact member 36, the timeof this operation depending upon the amountof change in the regulatedquantity from its desired value. Upon engagement of contact members 44and 46, a circuit is closed from the supply conductor it throughconductor 6i, cam switch 52, which is in its circuit closing positionwhen the tap-changing mechanism is at a tap position, through conductor63, contact members tit and it, conductor 64, the operating coil 22a ofthe secondary relay 22, and the conductor 66 to the supply conductor it.thus energizing the secondary relay 22 for operating it to a position toclose relay contacts 22b and 220 and cause operation of the motor it ina direction to raise the voltage supplied to conductors ii, l2 and. 93.

Upon the operation of the relay 22 to its circuit closing position, acircuit to energize the motor 89 is closed from the supply conductor itthrough conductor to the motor terminal 69, from the motor terminal llthrough conductor 12, relay contact member 220 of the ralay 22, andconductor iii to the supply conductor i3, causing the motor to operatein a direction to raise the regulated voltage. A holding circuit for therelay 22 is completed from the supply conductor l2 through conductor 6|,the cam switch'62, conductor 63, contact member 2212 on relay 22,through relay winding 22a and conductor 55, to supply conductor 63'. If,after the relay 22 has been operated to its circuit closing position,the voltage of the circuit it, i2, and i3 should be restored so that thprimary relay 20 operates to separate its contacts 44 and 46, the abovetraced holding circuit will hold the relay 22 closed to continue theoperation of the motor.

A circuit is also closed from supply conductor it through conductor it,relay contact member 220, conductor 12, the winding 24a of relay 24,through conductor it to supply conductor l2, thus causing the relay 24to operate to its circuit closing position. This operation of the relay24 closes contacts 24b, 24c, and 24d. The contact 2412 closes one pointin a circuit that is completed upon the closing of the cam switch 8i,and the contacts 240 and 24d close points in a circuit that is completedupon the closing of the cam switch 90.

When the relay "222 is closed, as above described, the motor it isenergized to operate the tapgames changing contact members fromengagement with one set of tap-changing switch contact members it to anadjacent one or the series of contact members it. Upon movement of themotor 19 and the shaft ii, the cams 82, 92, and 88 start to move. Aftera short time interval, the cam 82 moves the switch 8i to its circuitclosing position and causes it to remain closed until the shaft ll hasmade substantially one revolution corresponding to movement of thetap-changing mechanism from one tap-changing position to the n-iit.during a tap-changing operation a circuit is clos d rom. the supplycircuit conductor conductor cam switch 85', conductor contact member bof the relay 24 to a junction point 86, and from this junction pointthrough two branch circuits, one leading through the winding 285-: ofthe relay 24 as previously traced to the supply circuit condoctor 5 andthe other leading through conduster 12, motor terminals ii and $9, andconductor 58 to supply conductor 52, to maintain the operation of themotor until the completion of a step of operation or" the tap-changingmechanism.

The care and e relay 25 close prior to the opening of the switch 52 sothat the motor circuit through the contact 2% of relay 25 is establishedprior to interruption of the above traced holding circuit through thecam switch 62 and contact 2233 of the relay 22, which holding circuitenergizes the winding 22a that holds the contact 220 closed.

The cam switch 95 likewise is operated to a circuit closing position bythe cam 92 as the motor i9 moves from a tap position during atapchanging operation. The cam switch 9! would ordinarily be designed toclose after the cam switch M has closed and established the holdingcircuit. A circuit is thereby closed from supply conductor 12, throughconductor 90, cam switch 92, conductor 93, contact member 240 of therelay 28, conductor 94 through a winding 95 of the reactance device 28that is inductively related to the winding 21, through conductor 96,contact member Nd and resistor 98, to supply conductor i3, thusintroducing into the winding 2? a voltage for modifying the energizationof the primary relay operating winding 25 to increase the energizationof the relay and cause separation of the contact members 44 and W. Thisinsures that, unless a large change in voltage is called for requiringseveral tap-changing steps, when the tap-changing operation of one stephas been completed, the contact members 45 and 45 will be separated andthe relay 29 will not cause further operation of the tap-changingmechanism until sufficient time has passed for the effect of thetap-changing operation to be felt on the winding 26 to cause furtheroperation of the relay in response to the voltage across conductors l2and I3. The cam switch 9| opens, upon or slightly before the completionof a tapchanging operation, thus interrupting the circuit through thecontact members 240 and 24d of the relay 24 to the winding 95 of thereactance device 28 so that the relay 20 will again be responsive to thevoltage of the circuit being regulated when the tap-changing operationis completed. Upon completion of the tap-changing operation, the camswitch 8! is also opened, thus interrupting the motor energizing circuitthrough the contact member 2422 and the motor terminals ll and S9 tostop the motor 19. The opening of the cam switch 8! also deenergizes thwinding 24a so; do

oi the relay 24, thus permitting this relay to drop to its open circuitposition. 7

It the conditions of the regulated circuit re quire further operation orthe regulating mechanism, this will be effected by a further operationof the relay 2D, to again bring the contact memhere 4 and 48 again intoengagement, efiectlng a further operation of the tap-changing mechanismin the manner just described.

the regulated voltage rises above its desired value, the relay ill willoperate to bring the contact member or into engagement with the comember l a time interval depending upon the am rture oi the regulatedquantity fror Upon engagement of the rela, contact members 3 a '1 all, acircuit is closed "a the supply conductor through conduc switch 132?,members I nuctor is coil o Eliot. thv ope cult closing pc the meta rticn to lower '4 age supplied conductors and This circuit extends fromthe supply conductor l2 through conductor to the motor i559 and from thmotor terminal illd through concluctor Hid, relay contact member relay23, and conductor ill to the supply conductor ii'. A holding circuit forthe relay plated from the supply cor "or 62 I conductor 35, cam switchit, co.

the contact member 2% on relay tlnou relay winding and conductor to thesupply conductor ii after the relay has been operated to its circuitclosing position, the voltage of the circuit represented by conductorsl2, and 13 should be restored to its desired value so that the primaryrelay 2% operates'to separate its contact members 44 and til, the abovetraced holding circuit will hold the relay 23 in its closed position tocontinue the operation of the motor I9. This operating feature isprovided in order to prevent the motor from stopping except when thetap-changing mechanism is in one of its tap-changin positions connectingthe switch contact members 55 with one or the other of the plurality ofcontact members it.

Upon the closing of the relay 25), a circuit is also closed from thesupply conductor 93' through conductor ill, relay contact member 23c,conductor M, the Winding 25a of relay 25 through conductor it to supplyconductor it, thus causing the relay 25 to operate to its circuitclosing position. This operation of the relay 2& closes contacts 25b,25c, and 2562. The contact 2% closes one point in a circuit that iscompleted upon the closing of the cam switch ill and the contacts 250and 25d close points in a circuit that is completed upon the closing ofthe cam switch 9 i When the rela 23 is closed as above described, themotor 59 is energized to operate the tapchanging contact members illfrom engagement with one set of tap-changing switch contact mem hers i lto an adjacent one of the series of con tact members it. Upon movementor" the motor 59 and il the cams w closes the closed until the sh onerevolution ccrl spending to are accuser tap-changing mechanismi'rom onetap-changing position to the next. A circuit is closed from the supplycircuit conductor 83' through conductor 83, cam switch 9i, conductor 84,contact member 2517 of the relay 25, to a junction point I06, and fromthis junction point through two branch circuits. One of these twocircuits leads through the winding 25a of the relay 25 as previouslytraced to the supply circuit conductor l2, and the other leads throughconductor I04, motor terminals I03 and 69, and conductor 68 to supplyconductor I 2' to maintain the operation of the motoruntil thecompletionof a step of operation of the tap-changing mechanism.

The cam switch 8i closes before the cam switch 62 opens so that themotor circuit through the contact 25b of the relay 25 is establishedprior to the interruption of the holding circuit through the cam switch62 and the contact 2% of the relay'23, through which circuit the winding23a is energized to hold the relay 23 closed. The cam switch 9|islikewiSe operated to a circuit closing position by the cam 92 as themotor is moves from a tap-changing position during the tapchangingoperation. A circuit is closed bythe cam switch 9i extending from thesupply conductor i2, through the cam switch 9 i, conductor 93, contactmember 250 of the relay 2E, conductor 96, through the winding 95 of thereactance device 28, conductor 95, contact member 25d and resistor i 98to supply conductor it, thus introducing into the winding 27 a voltagefor modifying the energization of the primary relay operating winding 26to decrease the energization of the relay and cause separation of thecontact members it and ill. This insures that when the tap-changingoperation has been, completed, the contact members it and t? will beseparated and the relay 2!! will not cause further operation of thetap-changing mechanism until sufficient time has passed for the efiectof the tap-changing operation to be felt on the winding 29 so thatfurther operation of the tap-changing mechanism will be in response tothe voltage across the conductors i2 and it as impressed upon the relaywinding 25.

Upon'completion of the tap-changing operation, the cam switch 8i isopened, interrupting the motor energizing circuit through the contactmember 25!) and the motor terminals Hi3 and 69 to interrupt theoperation of the motor 59. The opening of the cam switch 90 alsodeenergizes the Winding 25a of the relay 25, thus permitting this relayto drop to its open circuit position. The cam switch 9! is likewiseopened as the tapliimted otherwise than by the scope sented in curves 1+and I- are calculated values based upon the assumption that theresistors 98 and I88, respectively, have a value equal to zero. Byvarying the value or these resistor elements, the magnitude oi thecurrent values 1+ .and I may be varied and, therefore. the voltage thatis induced from the'winding. 98 to the winding 21 may be controlled asrequired. In the curve, the turn ratio between windings 21' and 85 isplotted against the primary current in the relay circuit. It will benoted that for aturnratio of unity, both curves are a substantialdistance from the curve represented by the horizontal line Io, at whichvaiue a substantial "boost" or buck" volt age may be introduced into thecircuit of the relay winding 28 through the reactor device 28. It willbe noted that as the turn ratio between the windings 21 and 95increases, both curves I+ and I- rise above the curveIo.

It will be obvious to those skilled in the art that modifications in theapparatus and circuits illustrated and described may be made within thespiritof the invention, and we do not wish to be of .the appendedclaims.-

We claim as our invention:

1. In combination, apparatus for controlling an electrical quantity tobe regulated, regulating means iorregulating said electrical quantity ina series of predetermined regulating steps, control equipment for saidregulating means including an induction type circuit controlling relayhaving a movable disc of conducting material, a magnetic circuit havingpole pieces adjacent to the disc for controlling the operation of thedisc, and means for energizing the magnetic circuit responsive to thevalue of said electrical quantity for initiating a the operation of saidregulating'means, and switch controlled reactor means responsive to andeflective during the operation of said regulating means through aregulating step for biasing said circuit controlling relay in adirection tooppose continued operation or the regulating means uponchanging mechanism approaches a tap position interrupting the circuitthrough the contact members 25c and 25d of the relay 25, and the Winding95 of the reactance device 28.

If the conditions of the regulated circuit require further operation ofthe regulating mechanism in the same direction, this will be efiected bya further operation of the relay 29 to again bring the contact members44 and all into engagement, effecting a similar operation of themechanism from one tap position to the next.

Referring to Fig. 3, the curves 1+ and I indicate the current that willflow through the relay winding 26 as a result of the operation of thereactor device 28 when the one or the other of the relays 24 or 25 isclosed. The curve Io represents the current when the secondary, that is,the circuit of the winding 95, is open so that there is no inducedcurrent from the winding 95 to the winding 2?. The current valuesreprethe'completion of the operation of the regulator through aregulating step. I

2. In combination, apparatus for controlling an electrical quantity tobe regulated, regulating means for regulating said electricalquantlty ina. series of predetermined regulating steps, control equipment includingan electric motor and mechanism operated thereby for operating saidregulating means including an induction type circuit controlling relayhaving a movable disc of conducting material, a'magnetic circuit havingpole pieces adjacent to the disc for controlling the operation of thedisc and permanent magnets having pole pieces adjacent the disc forintroducing a time delay into the operation of the relay, and means forenergizing the magnetic circuit responsive to the value of saidelectrical quantity to be regulated for initiating the operation of saidregulating means, and circuit controlling switch means responsive to theenergization oi the electric motor for operation-in the one or the otherdirection for biasing said circuit controlling relay in a direction tooppose continued operation of the regulating means in the same directionupon the completion oi the operation thereof through a regulating step.

3. In a step type regulator, a circuit controller responsive tovariations from normal value of an electrical quantity to be regulated,control means controlled by said controller for initiating a correctionin the electrical quantity, and means responsive to the initiation ofthe correction in' the electrical quantity for biasing the controller ina direction to cause an interruption in the operation of the regulatorupon a completion of an operating step and to promptly interrupt themeans for biasing the controller upon the completion of an operatingstep of the regulator to thereby promptly condition the circuitcontroller for initiating iurther operation of the regulator in responseto variations in the electrical quantity from normal.

4. In combination, apparatus for controlling an electrical quantity tobe regulated, regulating means including motor operated mechanism forregulating said electrical quantity from one to another of a pluralityof predetermined operating steps, control means for said regulatingmeans including a contact making primary relay responsive to the valueof the electrical quantity to be regulated and additional meansincluding control circuits and contact members controlled by the primaryrelay for initiating the operation of said motor operated mechanism inthe one or in the other direction, switch controlled reactor meansresponsive to the operation of the motor operated mechanism for biasingthe operation of the primary relay to separate the contact membersthatinitiate the operation of the regulator, and cam operated switch meansfor interrupting the operation of said last-named means upon thecompletion of the operation of the motor operated mechanism through anoperating step of the regulator.

5. In a step type regulator, a circuit controller responsive tovariation in an electrical quantity to be regulated from a desiredvalue, a motor operated mechanism for varying the position of saidregulator, control means for controlling the operation of said motoroperated mechanism in the one or in the other direction including acontact making primary relay responsive to the value of the electricalquantity to be regulated, said primary relay including an operatingwinding connected in a circuit energized in accordance with theregulated electrical quantity, a reactance device having a windingconnected in said circuit, a circuit responsive upon the operation ofsaid motor operated mechanism for introducing a component of voltageacross said reactance device in a direction to bias the operation of theprimary relay against initiating another step of regulation in the samedirection, and for interrupting said circuit to remove said bias in theoperation of the primary relay upon completion the operation of theregulator through a regulating step.

6. In combination, apparatus for controlling an electrical quantity tobe regulated, a motor operated regulating means for regulating saidelectrical quantity in steps, a circuit controller responsive tovariations in the value of the electrical quantity to be regulated froma desired value for initiating the operation of said regulating means,said circuit controller including a primary relay including an operatingwinding connected in a circuit energized in accordance with theelectrical quantity to be regulated, a reactance device having a windingconnected in said circuit, an antihunting circuit for introducing acomponent of voltage across said reactance device for biasing theoperation of the primary relay, and circuit control means operative uponthe operation of said motor operated regulator means for so closing saidanti-hunting circuit as to bias the operation of the primary relayagainst initiating another step of regulation in the same direction, andfor interrupting said anti-hunting circuit upon com- 10 pletion of theoperation of the regulator through a regulating step.

7. In a regulator arranged to operate in a series 'of predeterminedoperating steps, regulator operating means for operating said regulator,a primary relay responsive to variations from normal of a condition tobe regulated for initiating the operation of said regulator operatingmeans for operating said regulator in the one or' in the otherdirection, mechanically operable switching means effective upon theinitiation of the operation of the regulator in the one or in the otherdirection from a step position for continuing the operation of theregulator in the given direction to complete an operating step of theregulator independently of the primary relay, switch controlled meansresponsive to the initiation of the operation of the regulatorin the one'or in the other direction and efiective during the operation of theregulator through a regulating step for v biasing the primary relay in adirection to cause an interruption in the operation of the regulatorupon a completion of an operating step and to promptly interrupt themeans for biasing the primary relay upon the completion of an operatingstep of the regulator. and switching means effective upon the completionof an operating step of the regulator for returning the control of theregulator to the primary relay for initiating further operation of theregulator in response to variations in the regulated condition fromnormal.

'8. In combination, an alternating-current circuit to be regulated,regulating mechanism for adjusting the voltage of said circuit inpredetermined operating steps, an electric motor for operating theregulating mechanism, control equipment for said motor including aprimary relay responsive to the value of the voltage of saidalternating-current circuit for initiating the operation of said motorin the one or in the other direction, electrically controlled switchingmeans independent of the primary relay and effective upon the initiationof the operation of the motor in the one or in the other direction forcontinuing the operation of the motor to complete an operating step ofthe regulating mechanism, and electrically operated switch controlledmeans responsive to and effective during the operation of the regulatingmechanism through an operating step for biasing the primary relay in adirection to oppose continued operation of the regulating mechanism inthe same direction upon the completion of the operation thereof througha regulating step.

9. In combination, an alternating-current circuit to be regulated, meansincluding a transformer for supplying alternating-current energy to saidcircuit, tap-changing mechanism for adjusting the voltage supplied tosaid alternatingcurrent circuit, regulating means for controlling theoperation of the tap-changing mechanism through successive tap-changingsteps of operation, each step of operation being effective for changingthe connection of the alternating-current circuit from one transformertap connection to another, control equipment for said tapchangingmechanism including a contact making primary relay and a control circuittherefor responsive to the voltage of said alternating-current circuitfor initiating the operation of the tap-changing mechanism, electricallycontrolled means including a cam operated switch responsive toinitiating the operation of the tap-changi i ing mechanism for causing acontinuation of the operation thereof through an operating step of themechanism independently oi the primary argeee 12 mg the control or thetap-changing mechanism to the primary relay. I

HERBERT J. CARLIN. JAMES F. CHAPMAN.

REFERENCES CITED The following references are of record in the tile ofthis patent:

UNITED STATES PATENTS Number Name Date 1,936,801 Nycum Nov. 28, 19332,254,039 Kovalsky A118. 26, 1941

